The present invention relates generally to an exposure apparatus and method used to fabricate various device including semiconductor chips such as ICs and LSIs, display devices such as liquid crystal panels, sensing devices such as magnetic heads, and image pickup devices such as CCDs, as well as fine patterns used for micromechanics, and more particularly to an immersion exposure apparatus (an immersion lithography exposure system) and method for exposing the object through the fluid between the projection optical system and the object.
A projection exposure apparatus has been conventionally used to transfer a circuit pattern on a reticle (or a mask) via a projection optical system onto a wafer etc, and the high-quality exposure at a high resolution has recently been increasingly demanded. The immersion exposure attracted people's attentions as one means that satisfies this demand. The immersion exposure promotes the higher numerical aperture (“NA”) by replacing a medium (typically the air) at the wafer side of the projection exposure with fluid. The projection exposure apparatus has an NA=n·sinT where n is a refractive index of the medium, and the NA increases when the medium that has a refractive index higher than the air's refractive index, i.e., n>1.
For the immersion exposure, some methods have already been proposed to fill the fluid in the space between the object and the projection optical system (see, for example, International Publication No. WO99/49504.). International Publication No. WO99/49504 proposes to provide a fluid supply nozzle and a fluid recovery nozzle near a final lens in the projection optical system that is closest to a substrate, and supplies fluid from the fluid supply nozzle between the substrate and the final lens. The exposure is performed, while the fluid supply nozzle continuously supplies the fluid and the fluid recovery nozzle continuously recovers the fluid or while the fluid circulates between the substrate and the final lens. If new fluid is always supplied, it is desirable because there is little change in the transmittance and refractive index of the fluid even if a resist and an optical element begin to dissolve into the fluid.
The immersion exposure causes the air bubbles and the micro bubbles (these are only called “air bubbles” in this application) to mix into the fluid, when exposing the transfer area around the substrate and filling the fluid in the space between the substrate and the final lens. The air bubbles shield the exposure light, resulting in lowered transfer accuracy and yield, and cannot satisfy the demand for the high-quality exposure. The air bubbles would never be eliminated completely irrespective of the subsequent continuous supply and recovery of the fluid. Moreover, the air bubbles are generated from the fluid supply nozzle, and might mix with the continuously supplied fluid.
A method for immersing a chuck to fix the substrate to a stage as a driving part in the fluid, a method for immersing the chuck and the stage, and a method for filling in a wafer cassette that stores the wafer with the fluid, etc, are known as the other fluid supply methods (see, for example, Japanese Patent Application Publication No. 10-303114). However, it is a common problem for all the fluid supply methods to prevent the air bubbles being mixed with the fluid.
To solve this problem, a method for vibrating the fluid, the substrate, and the optical element of the projection optical system by irradiating an ultrasonic wave to the fluid and removing the air bubbles is proposed (see, for example, Japanese Patent No. 2753930, Japanese Patent Application Publication No. 11-176727, U.S. Pat. No. 5,610,683, Japanese Patent Application Publication No. 2001-250773, U.S. Pat. No. 6,610,168, Japanese Patent Application Publication No. 11-54427, Japanese Patent Application Publication No. 8-8216, Japanese Patent Application Publication No. 2003-31540, Japanese Patent Application Publication No. 2000-216126, Japanese Patent Application Publication No. 10-303161, and Japanese Patent Application Publication No. 2002-248429).